Magnetic circuit

ABSTRACT

A magnetic circuit for a voice coil, comprising, a magnet cup with a one sided open cylindrical shape with a base. The magnetic circuit further includes a conical magnet with a side including a partial conical shape. The magnetic circuit includes a pole shoe which has a side with a recessed conical shape corresponding to the conical shape of said magnet. The magnet cup, the conical magnet and the pole shoe are stacked so that the conical magnet is centrally arranged on the base inside said magnet cup, the pole shoe is arranged on the conical magnet so that the side with a recessed conical shape of the pole shoe is in contact with the side with a conical shape of the conical magnet, such that an air gap is obtained between an inner wall surface of the magnet cup and the stacked conical magnet and the pole shoe.

RELATED APPLICATIONS

The present application claims the benefit under 35 U.S.C. §119(e) ofU.S. Provisional Patent Application 61/726,962 filed Nov. 15, 2012titled “PROGRESSIVE PUMP FORCE REGULATION,” U.S. Provisional PatentApplication 61/726,965 filed Nov. 15, 2012 titled “EXTENDED ELASTICITYOF PUMP MEMBRANE WITH CONSERVED PUMP FORCE,” and U.S. Provisional PatentApplication 61/727,012 filed Nov. 15, 2012 titled “Magnetic Circuit,”each of which applications is hereby incorporated herein by reference intheir entirety.

The present application also claims a priority benefit claims thebenefit under 35 U.S.C. §119 of European Patent Application 12192847.7filed Nov. 15, 2012 titled “PROGRESSIVE PUMP FORCE REGULATION,” EuropeanPatent Application 12192859.2 filed Nov. 15, 2012 titled “EXTENDEDELASTICITY OF PUMP MEMBRANE WITH CONSERVED PUMP FORCE,” and EuropeanPatent Application 12192889.9 filed Nov. 15, 2012 titled “MagneticCircuit,” each of which applications is hereby incorporated herein byreference in their entirety.

It is appreciated that the embodiments disclosed in each of theapplications above may be combined in and/or utilized in combinationwith one another. For instance, one or more of the embodiments and/orone or more elements of embodiments described in conjunction with the“PROGRESSIVE PUMP FORCE REGULATION” application may be combined and/orused in combination with one or more embodiments or elements ofembodiments described in conjunction with the “EXTENDED ELASTICITY OFPUMP MEMBRANE WITH CONSERVED PUMP FORCE” application and/or the“Magnetic Circuit” application.

BACKGROUND

1. Field of the Disclosure

This disclosure pertains in general to voice coil. More particularly thedisclosure relates to voice coils for driving membrane pumps used, forexample, as sampling pumps in devices for patient monitoring, breathmonitoring, anaesthesia monitoring, especially for medical ventilationmonitoring and gas analyzers for monitoring gas composition in patient'sbreathing.

2. Description of the Related Art

The common way of designing a magnetic circuit, such as for a voicecoils, is to make the magnet strictly cylindrical and if a pole shoe isused it is normally strictly cylindrical too. The pole shoe is used tocollect the magnetic flux and redirect it to a pure radial direction.The density of the magnetic flux inside the steel parts (magnet cup andpole shoe) is depending of the section area of the parts. If it is tooconcentrated, the steel will be saturated and not able to conduct anymore flux which leads to both leakage of magnetic flux (i.e. immediatemagnetic material will be attracted) and limit the circuit's capacity.The cylindrical design of the magnet cup is also limiting the voice coilto have a mount of its free shaft end outside this cylindrical outershape.

Hence, a new improved design of a magnetic circuit with better directingcapability of the flux would be advantageous, especially if the samemagnetic circuit has a small volume.

SUMMARY

Accordingly, embodiments of the present disclosure preferably seek tomitigate, alleviate or eliminate one or more deficiencies, disadvantagesor issues in the art, such as the above-identified, singly or in anycombination by providing a device, system or method according to theappended patent claims for providing an improved magnetic circuit, suchas in voice coil devices. These voice coils may be used in membranepumps for patient monitoring, breath monitoring, anaesthesia monitoring,especially for medical ventilation monitoring and gas analyzers formonitoring gas composition in patient's breathing.

Disclosed herein are device, system and methods for providing theimproved magnetic circuit.

According to one aspect of the disclosure, a magnetic circuit for avoice coil includes a magnet cup which has a one sided open cylindricalshape with a base, the base has an inner surface, a conical magnet whichhas a side with an at least partial conical shape, and a pole shoe whichhas a side with a recessed conical shape corresponding to the conicalshape of the conical magnet, is disclosed. The magnet cup, the conicalmagnet and the pole shoe are stacked so that the conical magnet iscentrally arranged on the base inside said magnet cup, then the poleshoe is arranged on the conical magnet so that the side with a recessedconical shape of said pole shoe is in contact with the side with aconical shape of said conical magnet. The stack is arranged such that anair gap is obtained between an inner wall surface of the magnet cup andthe stacked conical magnet and said pole shoe.

The conical shape allows for a better distribution of magnetic fluxinside the pole shoe. The design also improves the assembly of themagnetic circuit, as the conical shape allows for a self-alignmentbetween the conically shaped parts.

In some examples of the disclosure, the base has an inner surface areawith a partially conical shape protruding inward the magnet cup and theconical shape is at a central portion of the base of the cylindricalshape. Further, the conical magnet has a second side with a recessedconical shape corresponding to the conical shape of the inner surfacearea of base.

By having a conical shaped interface between the conical magnet and theinner surface of the magnet cup improves the distribution of themagnetic flux in the magnetic circuits.

Even further, by having all three parts conically shaped improves theself-alignment properties of the stack even further.

In some examples of the disclosure the base has an outer surface with arecessed conical shape.

Moreover, the conical shape of the base makes it possible to have arecessed outer surface of the base which creates a space which may beused to add a support for a free shaft end without adding any volumeoutside the cylindrical volume. Hence the voice coil may be smaller insize.

An airgap may be obtained between an inner surface area of thecylindrical shape of the magnet cup and the outer surface of the stackedconical magnet and the pole shoe. In this airgap a coil may be arranged.

In some examples is the coil entwined by self-adhesive lining. Thisdesign may take advantage of the limit space of the airgap. Hencesmaller voice coils are possible to design.

In some further examples, a bore may go at least partially through theheight of the stack. The bore is preferably arranged at the centre ofthe stack. In this bore a shaft may be arranged. The shaft may beconnected to the coil so that when the coil moved the shaft will move.The motion of the shaft is a linear reciprocating stroke motion.

In some examples of the disclosure, the angle of the conical shapesspans the range 10 to 45 degrees.

Some materials of which the conical magnet may be made of are neodymium,samarium-cobalt, or alnico.

The pole shoe and the magnetic cup may be made of Ferromagnetic metalsand/or alloys.

According to another aspect of the disclosure, a membrane pump isdisclosed. The membrane pump comprises a magnetic circuit in accordancewith the disclosure herein, a pump housing with a chamber having an openend. The membrane pump also includes a membrane element having a firstarea arranged to cover the open end of the chamber. The magnetic circuitis arranged and adapted to transfer a force by a stroke motion on themembrane.

In some examples of the membrane pump, the membrane element comprises acentral section with a second area surrounded by a periphery section.The central section is thicker than the periphery section, and thesecond area of the central section is smaller than a third area of theopen end of the chamber of which the central section is arranged over.

The advantages with this disclosed configuration is that it prevents thestroke from hitting the bottom of the chamber since a pump stroke isdecelerated in a progressive way which not only makes the stop silentbut also reduces the mechanical vibrations and keep them to a minimum.Further, the deceleration reduces the effective pump area of themembrane closer to the end of a stroke. Since the force of the stroke isconstant, the pump becomes stronger closer to the end of the stroke.

In some further examples, the chamber may have bevelled inner walls. Thecentral section of the membrane element is centrally arranged over theopen end and the first area of the membrane element is larger than thethird area of the open end.

Also, in some examples the pump housing may have an enlarged surfacesurrounding the open end of the chamber with a total area having atleast the same size as the membrane element.

In some further examples of the disclosure, the membrane element isslidably clamped between the elongated surface of the pump housing and asecond member of the pump housing.

The advantages with this configuration are that by holding a membraneelement slidably fixed at a larger diameter than the actual workingdiameter (area) is that the membrane if free to move radial and stretch.Hence a longer pump stroke may be achieved (i.e. more volume can bepumped per stroke). Also a longer life of the membrane due to lowerfatigue stress levels and more effective use of the available pump forcemay be obtained.

According to a further aspect of the disclosure, a method for assemblingpart to a magnetic circuit is disclosed. The method comprises, utilizinga conical design of the parts and a magnetic force of the magneticcircuit to allow different parts to self-orient.

The conical shape allows for a much easier assembly operation since theshape makes the parts self-orienting.

In this disclosure the word “conical” is defined both as strictlyconical but also as a truncated cone.

It should be emphasized that the term “comprises/comprising” when usedin this specification is taken to specify the presence of statedfeatures, integers, steps or components but does not preclude thepresence or addition of one or more other features, integers, steps,components or groups thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects, features and advantages of which examples ofthe disclosure are capable of will be apparent and elucidated from thefollowing description of embodiments of the present disclosure,reference being made to the accompanying drawings, in which

FIGS. 1A and 1B are illustrating cross-sectional schematic overviews ofexamples of a magnetic circuit;

FIGS. 2A and 2B are illustrating cross-sectional schematic overviews offlux distribution in a prior art circuit and an example of the disclosedcircuit;

FIGS. 3A and B are illustrating cross-sectional schematic overviews ofsimulated flux distribution in a prior art circuit and an example of thedisclosed circuit; and

FIG. 4 is illustrating a cross-sectional schematic overview of amembrane pump.

DESCRIPTION OF EMBODIMENTS

Specific examples of the disclosure now will be described with referenceto the accompanying drawings. This disclosure may, however, be embodiedin many different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the disclosure to those skilled in the art. Theterminology used in the detailed description of the embodimentsillustrated in the accompanying drawings is not intended to be limitingof the disclosure. In the drawings, like numbers refer to like elements.

The following description focuses on an embodiment of the presentdisclosure applicable to a magnetic circuit and to a voice coil. Thevoice coil is to be used as an actuator. For example, the voice coil maybe used as an actuator for a membrane pump, such as a sampling pump indevices for patient monitoring, breath monitoring, anaesthesiamonitoring, especially medical ventilation monitoring and gas analyzersfor monitoring gas composition in patient's breathing. However, it willbe appreciated that the description is not limited to this applicationbut may be applied to many other systems where a fluid pump is required.

FIG. 1A is a magnetic circuit 100. The magnetic circuit comprises amagnet cup 7 which have a one sided open cylindrical shape with a base.The base is partially conical and the cone is directed inward thecylinder. The cone shape is located at a central portion of the base ofthe cylinder. The magnetic circuit 100 also comprises a conical magnet 8and a pole shoe 9. The pole shoe 9 has one side which has a conicalshape being directed inwards. These three components are stacked so thatthe conical magnet 8 is arranged on the base, inside the magnet cup 7.The pole shoe 9 is then arranged on the conical magnet 8.

Additionally, when arranged in this fashion an airgap 11 is obtainedbetween an inner surface area 20 of the cylinder and one side of theparts stacked inside the magnetic cup 7.

In this airgap, a coil (not seen in the figure) may be arranged. In someexamples of the magnetic circuit, the coil is entwined by self-adhesivelining. This design may take advantage of the limit space of the airgap.Hence a smaller design of the magnetic circuit is possible.

Alternatively to the illustration in FIG. 1A, only the interface betweenpole shoe 9 and the conical magnet 8 may be conical.

By using a pole shoe 9 in the magnetic circuit 100 wherein the pole shoe9 having a recessed conical shape in contact with a correspondingconical shape of an conical magnet, the magnetic flux inside the coniclamagnet 8 is purely axial. Thus all of the flux is transferred into thepole shoe 9 and the magnet cup 7. Since the flux inside the pole shoe 9is redirected towards the magnetic cup 7 the flux density is lowercloser to the cylindrical centre than at the outer side. It is thereforean advantage to make the design conical since this also allows for alarger sized magnet, if desirable.

As illustrated in FIG. 1B the magnetic cup 7 does not need to have aconical recess on an outer surface of the base.

On the other side, if also the magnets 8 other side (the one facing themagnet cup 7) is made conical and the base of the cup shape 7 too (likein FIG. 1), a small conical space is created which is suited to host agood flexible support for the oscillating free voice coil shaft withoutrequiring any extra space for this necessary feature.

Some examples of magnetic materials, from which the conical magnet 8 maybe made of, are neodymium, samarium-cobalt, or alnico. The pole shoe 9and the magnetic cup 7 may be made of ferromagnetic metals and/oralloys.

Additionally, in some examples of the magnetic circuit 100 in FIGS. 1Aand 1B, the angle 10 of the conical shapes span the range from 10 to 45degrees.

Additionally and/or alternatively if also the interface between theconical magnet 8 and the inner surface of the base of the magnetic cupis conical, such as illustrated in FIG. 1A and 1B, the angle 15 may alsobe from 10 to 45 degrees.

The angles 10 and 15 may have the same gradient or the angles 10 and 15may have different gradients.

The thickness proportions of between different part such as the wall ofthe magnetic cup 7 and the pole shoe 9 in regard to magnetic flux,depends on the grad and strength of the magnet. But it also depends onthe function of the magnetic circuit and the cylindrical section area.

In some examples of the magnetic circuit 100, the stack of parts mayhave a bore 6 going at least partially through. The bore 6 is arrangedat the centre of the stack. A shaft connected to the coil in the airgap11 may be arranged in the bore 6. When driving a voltage or currentthrough the coil shaft will move linear in a reciprocating strokemotion. This can be utilised as a pump head to exert a force on amembrane of a membrane pump.

Also, assembling a voice coil magnetic circuit requires muchcarefulness. It is absolutely necessary to assemble the magnet and thepole shoe concentric to make it work. This can be very tricky since themagnet forces always pulls the magnet and pole shoe towards thecylindrical wall of the magnet cup. By using the conical design of theparts, the magnetic circuit becomes self-oriented. The magnetic forcewill pull the conical parts together at the centre of the cup asintended. Hence this effect may be improved if all three parts haveconical shapes.

FIGS. 2A and 2B are schematically illustrating the magnetic fluxdistribution in a prior art (FIG. 2A) magnetic circuit 200 and in anexample of the disclosed (FIG. 2B) magnetic circuit 100.

FIGS. 3A and 3B are simulations to schematically illustrate the magneticflux distribution in a prior art (FIG. 3A) magnetic circuit 200 and inan example of the disclosed (FIG. 3B) magnetic circuit 100. The scalesof the simulations are not the same so FIGS. 3A and 3B are only used forthe purpose of illustrating the differences in magnetic fluxdistribution.

FIG. 4 illustrates a cross-sectional view of an example of a membranepump 300. The membrane pump 300 comprises a membrane element 33 a pumphousing 1, and optional second housing member 5 (e.g. membrane fixingplate) and a pump chamber 21. In this example, the pump chamber 21 hasbevelled walls for abutting an area where the membrane element 33becomes thicker. Hence decelerate the pump stroke in a progressive way.

A portion of the membrane may be slidably clamped between the secondmember 5 and the pump housing 1. This allows the membrane to move radialand stretch when a force is applied.

The advantages with this configuration are that by holding a membraneelement slidably fixed at a larger diameter than the actual workingdiameter (area), the membrane is free to move radial and stretch. Hencea longer pump stroke may be achieved (i.e. more volume can be pumped perstroke). Also, due to the radial movement, the same pump volume can bemaintained with less stretching which will increase the life of themembrane due to lower fatigue stress levels and more effective use ofthe available pump force may be obtained.

Additionally and/or alternatively, by designing the edge of the secondpump housing member 5 (i.e. membrane fixing plate) to be conical or withone or more radii positioned in the area where the membrane element 32becomes stiffer (thicker) it may also be possible to decelerate the pumpstroke in a progressive way. This will make the stops, when the membraneelement is in its turning point silent and also reduces the mechanicalvibrations due to the progressive motion deceleration.

The pump further comprises a pump head 12. In this example, the pumphead 12 is abutting the central section of the membrane element 33.Alternatively, in some examples, the pump head may be mechanicallyattached to the top of central section, such as inserted into thecentral section or a screw could be used to secure them together. Whenusing a pump head 12 abutting the top of the central section an adhesivemay be used between the top of the central section and the abutting areaof the pump head 12 to affix the two members. Examples of adhesives maybe, glue, sticky tape, etc.

In this example depicted in FIG. 4, the actuator exerting a force on themembrane element 33 is a voice coil. The voice coil is used to transmita reciprocating stroke motions by the pump head 12 to the membraneelement 33. Specifically, the voice coil may be a cylindrical voicecoil.

In one example, the coil 13 is a circular cylinder structure, which isfixed on the pump head 12 and placed in an air gap. The air gap isenclosed by a magnetic cup with conical bottom 7, a conical magnet 8,such as a permanent magnet, and a one side conical pole shoe 9.

Additionally, in order to maximize the utilization of the magnetic fieldin the air gap and reduce the size of the pump 300, the coil 13 may be askeletonless coil, entwined by self-adhesive lining. This design maytake advantage of the limit space of the air gap, hence it's possible todesign smaller membrane pumps 300.

In the example illustrated in FIG. 4, the magnet cup with a conicalbottom 7 is positioned as an inverted M-shape. The contact surfacebetween the conical pole shoe 9, the conical magnet 8 and the contactsurface between the conical magnet and conical bottom of the magnet cup7 are all tapered. The tapered surfaces are tapered in the samedirection. Such structure increases the side area of the conical poleshoe 9, making the magnetic field in the air gap distribute evenlyradially.

This design allows for a larger magnet, better distribution of themagnetic flux inside the pole shoe 9. Further, the conical shapeprovides better support for the free shaft of the pump head 12 withoutadding any volume outside of the cylinder volume. Thus the magneticfield is as large as possible when the coil 13 works in the air gap.

In FIG. 4, the working principle of the membrane pump 300 is: the coil13 positioned in the magnetic field formed by the one side conical poleshoe 9, the conical magnet 8 and the magnet cup with conical bottom 7.When an alternating voltage is transmitted to the coil 13, the coil 13will produce an alternating ampere force to drive the pump head 12 inreciprocating linear motion.

The pump cycle will produce a cycle of positive and negative pressure inthe pump chamber 21. When pressure in the sealed room is negative, fluidwill move through a pump inlet into the chamber 21. When pressure in thesealed room is positive, the pump 300 will move fluid out through anoutlet.

In the example illustrated in FIG. 4, a small voice coil is adopted todrive membrane to do linear motion so that large transmission mechanismsare eliminated. Thus the size of the membrane pump 300 is reduced. Thevoice coil does not affect the working life of the pump 300, because thevoice coil does not comprise structures that are easily worn out. Thevoice coil drives the membrane element 33 directly without the processof transforming motion to another; hence no intermediate energy isconsumed. Further, there is no starting torque problem; hence the pump300 may start almost instantly by applying a small voltage. The voicecoil therefore also output a force or a displacement of the pump head 12to collect a small volume of fluid even at small driving voltage orcurrent.

Also, the reciprocating motion of the pump head 12 is controlled bycontrolling the frequency of the voltage. Because the magnitude ofreciprocating motion is dependent to the amplitude of the current, thecollected flow size may be easily controlled by adjusting the amplitudeof the voltage to the voice coil.

While several embodiments of the present disclosure have been describedand illustrated herein, those of ordinary skill in the art will readilyenvision a variety of other means and/or structures for performing thefunctions and/or obtaining the results and/or one or more of theadvantages described herein, and each of such variations and/ormodifications is deemed to be within the scope of the presentdisclosure. More generally, those skilled in the art will readilyappreciate that all parameters, dimensions, materials, andconfigurations described herein are meant to be exemplary and that theactual parameters, dimensions, materials, and/or configurations willdepend upon the specific application or applications for which theteachings of the present disclosure is/are used. Also, different methodsteps than those described above, performing the method by hardware, maybe provided within the scope of the disclosure. The different featuresand steps of the disclosure may be combined in other combinations thanthose described. The scope of the invention is only limited by theappended patent claims

1. A magnetic circuit for a voice coil, comprising: a magnet cup including a one-sided open cylindrical shape with a base, said base including an inner surface; a conical magnet including a least one side with an at least partial conical shape; and a pole shoe including a side with a recessed conical shape corresponding to said conical shape of said conical magnet, wherein said magnet cup, said conical magnet, and said pole shoe are stacked so that said conical magnet is centrally arranged on said base inside said magnet cup, said pole shoe is arranged on said conical magnet so that said side with a recessed conical shape of said pole shoe is in contact with said side with a conical shape of said conical magnet, and said stack is arranged such that an air gap is obtained between an inner wall surface of said magnet cup and said stacked conical magnet and said pole shoe.
 2. The magnetic circuit of claim 1, wherein said base has an inner surface area with a partially conical shape protruding inward, wherein said magnet cup and said conical shape are at a central portion of said base of said cylindrical shape, and wherein said conical magnet has a second side with a recessed conical shape corresponding to said conical shape of said inner surface area of said base.
 3. The magnetic circuit of claim 2, wherein the base has an outer surface with a recessed conical shape.
 4. The magnetic circuit of claim 1, wherein a coil is arranged in said air gap.
 5. The magnetic circuit of claim 4, wherein said coil is entwined by self-adhesive lining.
 6. The magnetic circuit according to claim 1, wherein said stack has a bore going at least partially through and said bore is arranged at the centre of said stack.
 7. The magnetic circuit of claim 6, wherein a shaft is arranged in said bore, and said shaft is connected to said coil.
 8. The magnetic circuit of claim 7, wherein said shaft is linearly movable in a reciprocating stroke motion.
 9. The magnetic circuit according to claim 1, wherein the angles of said conical shapes span the range 10 to 45 degrees.
 10. The magnetic circuit according to claim 1, wherein said conical magnet is made of at least one of neodymium, samarium-cobolt, and alnico.
 11. The magnetic circuit according to claim 1, wherein said pole shoe and said magnetic cup are made of ferromagnetic metals or alloys.
 12. A membrane pump, comprising: a magnetic circuit for a voice coil, including: a magnet cup including a one-sided open cylindrical shape with a base, said base including an inner surface; a conical magnet including a least one side with an at least partial conical shape; and a pole shoe including a side with a recessed conical shape corresponding to said conical shape of said conical magnet, wherein said magnet cup, said conical magnet, and said pole shoe are stacked so that said conical magnet is centrally arranged on said base inside said magnet cup, said pole shoe is arranged on said conical magnet so that said side with a recessed conical shape of said pole shoe is in contact with said side with a conical shape of said conical magnet, and said stack is arranged such that an air gap is obtained between an inner wall surface of said magnet cup and said stacked conical magnet and said pole shoe; a pump housing comprising a chamber with an open end; and a membrane element including a first area arranged to cover said open end of said chamber, wherein said magnetic circuit is arranged and adapted to transfer a force by a stroke motion on said membrane.
 13. The membrane pump according to claim 12, wherein said membrane element comprises a central section with a second area surrounded by a periphery section, wherein said central section is thicker than said periphery section, and wherein said second area of said central section is smaller than a third area of said open end of said chamber of which said central section is arranged over.
 14. The membrane pump according to claim 13, wherein said chamber comprises a bevelled inner wall; and wherein said central section of said membrane element is centrally arranged over said open end, and said first area of said membrane element is larger than said third area.
 15. The membrane pump according to claim 12, wherein said pump housing has an enlarged surface surrounding said open end of said chamber with an area having at least the same size as said first area of said membrane element.
 16. The pump according to claim 15, wherein said membrane element is slidably clamped between said elongated surface of said pump housing and a second member of said pump housing.
 17. A method for assembling a magnetic circuit for a voice coil, comprising: providing a magnetic cup with a one-sided open cylindrical shape with a base, said base including an inner surface; providing a conical magnet including at least one side with an at least partial conical shape; providing a pole shoe including a side with a recessed conical shape corresponding to said conical shape of said conical magnet; stacking said magnet cup, said conical magnet and said pole shoe so that said conical magnet is centrally arranged on said base inside said magnet cup, said pole shoe is arranged on the conical magnet so that said side with a recessed conical shape of said pole shoe is in contact with said side with a conical shape of said conical magnet, and said stack is arranged such that an air gap is obtained between an inner wall surface of said magnet cup and said stacked conical magnet and said pole shoe, wherein said magnet cup, said conical magnet and said pole shoe are configured to magnetically self-align when stacked. 